Aluminum welding fluxes



Patented May 8, 1951 Mike A. Miller and Warren E. Haupin -New 'Ken sington, Pa., assignors to Aluminumflompany;

of America, Pennsylvania Pittsburgh, Pa.,'. a' corporation of No'Drawing. Application January'lS; 1949, Serial No. 71,224-

7 Claims. (01. 14826) This invention relates. to. aluminum. welding fluxes,.particularly fluxessuitable for coating. aluminum arc welding rods. Such fluxes should be capable of forming adherent coatings. on.alumi:- num arc welding rods, if they are to be applied as coatings; they shouldhave a suitable effect upon the characteristics ofrthe welding arc; and

they should produce slags that are readily removed from the work; The; fluxes of the invention are especially effective as coatings on aluminum rods for metallic arc welding of. alumi+ num, but they may also be appliedin powdered form and in welding processes other than arc welding. Because of the numerous advantages arising from the use of our fluxes in the metallic arc welding of aluminum, the problems in such applications thereof -will be first discussed.

Metallic arcwelding of aluminum has always been beset by difllculties; the welding rod must be manipulated carefully to obtain smooth deposits of metal'and' good welds. These dilficul-- ties are largely attributable to the fact that the: welding arc is unstable; metal'transfer from rodt to work tends totakeplace unevenly and the'arc tends to sputter and blow. Bycontrastthe me:-

tallic arc welding of steel has-been comparatively free of these difli'culties', the arc beingrelativelyo stable and the metal transfer smooth. The principal object of the invention, therefora'is to provide welding fluxes suitablefor use in the metallic arc welding of aluminum and capable of effectively stabilizing the arc.

Another difliculty in the metallicarcwelding.

of aluminum arises from the customary use of:

rods having flux coatings produced from water" containing flux mixtures; The moisture in such: flux coatings vaporizes and decomposes in the Welding process and, consequently, causes the Weld metal to be porous, although it appears to have the favorable effect'of making the are a forceful one. To avoid producing porous welds it is necessary to eliminate moisture from fluxcoatings, but such elimination of moisture ordinarily results in a decrease in the arc force, exaggerating the instability of the arc. The result is that molten metal accumulates on the: rod and then transfers to the work in large drops. or globules, with short-circuiting and'violent-energy surges. Since it is desirable (and often necessary) to employ dry flux coated rods, it is a further object of the invention to provide welding fluxes suitable for use in themetallic arc Welding of aluminum and capable" of effectively stabilizing the are even in the absence of moisture. A stable arc is necessary for satisfactorywelding, especially if: thearcdoes not have the" force characteristic.which'isaexhibited when there is moisturein the flux.v

Azgenerallobject of the invention is; of course,-v to provide multi-purpose aluminum" welding; fluxes; and a'more-particular object is to pro"- vide: fluxes especially suited to various processes for. arc welding aluminum. A further: object isto provide aluminumweldin'g fluxes which may;

be used: to produce: adherent coatings on: aluminum Weldingtrods, coatings which are sufiiciently flexible. SOL thattliey will r not readily flake, crack or. chip from the. rod; Al still further and'imr' portant object is to provide aluminumr welding fiuxes which will. not produce tenaciousislags on the: Work; in whatever form: such fluxes. are ap plied;

We. have? discovered certain new fluxes that are. generally suitable for: aluminum welding;v and particularly suitable. for arc welding aluminum by methods; employing'eitheribare: or coated? rods. They. may: be employed: in: powdered form and supplied directly to*the= welding. zone, or they; may be employed 'as coatings: on aluminum rods. Further; these fluxes adhere well to aluminum" welding rods when employed as coatings; thereon; they stabilizethe: welding are so as to efiect soft, quiet, but steady current flow: and transfer ofmolten' metal; even inlthe absence of moisture: they do not induce porosity; inthe weld whenemployed dry; andthey do not produce difiicultly-- removableslags-onithe work;

Generally: stated; our new' fluxes.- have as the vehicle components thereof at least two alkali metal chlorides, and have asthe'essential; com-- plementary componentssthereof lithium fluoride; aluminum fluoride and magnesiumafluoride. They; may, also" contain relatively small amounts of,- other: materials; particularly? as hereinafter recommended: The: aforesaid chlorides serve as a vehicle for the: aforesaid fluorides and; consti tuterthesprincipal weight of any given flux while: the aforesaid flllOI'ldSi serve: as essential; fluxing:

agents in an arc stabilizingcombination and rides, which are none-hygroscopic alternates; it follows that fluxes composed principally, or entirely; of "non-hygroscopic salts-may-be made upi Sincelithium chloride" may: be avoided in favor of sodiumv and potassium ch10- Such fluxes are very desirable since they take up the least moisture and can be readily dried, if necessary. Excellent flux coated aluminum welding rods can be made by melting and dehydrating a flux made up of non-hygroscopic salts, and then dipping the aluminum rods in the molten flux bath so that they acquire dry fused coatings. Thereafter it is possible to store or package the fused flux coated rods in a dry atmosphere, so that even small amounts of moisture are not picked up by the flux coating.

Further as to the fluorides, it should be noted that complex fluorides and appropriate combinations of single fluorides are interchangeable for the purpose of providing the essential fluorides in our fluxes. For convenience, however, single fluoride weights will be referred to in specifying the compositions of our fluxes. Complex fluorides that may be formed from single fluorides will not usually be specified herein, it being understood that two or more combinable single fluorides ma} form one or more complex fluorides, although the fluoride proportions specified will usually permit of there being an excess of one or more of the single fluorides.

The composition ranges for the fluxes of the invention will now be set forth. The principal weight of any flux should be provided by the alkali metal chlorides, these being the vehicle components of the flux. More specifically, the total amount of the alkali metal chlorides should be atleast50 per cent by weight of the entire flux, and less than about 85 per cent (preferably 60 to I per cent). As with other aluminum welding fluxes having an alkali metal chloride vehicle, two or more such chlorides may be employed, each in individual amounts between about and 60 per cent, to provide the total amount required. We prefer to employ sodium chloride and potassium chloride, which may conveniently and effectively be present in amounts of about 20 to 40 per cent by weight of sodium chloride (preferably 25 to 35 per cent), and about 25 to 45 per cent of potassium chloride (preferably 30 to 40 per cent). Itxis: often preferable to use a slightly greater amount of potassium chloride than sodium chloride; but approximately equal parts of these chlorides are usually satisfactory.

The major portion of the balance of the weight of any flux (over and above the alkali metal chloride weight) should be provided by the following fluorides: lithium fluoride, aluminum fluoride and magnesium fluoride, these being the essential complementary components of the flux.

More specifically, the total amount of these essential fluorides shouldbe at least about 15 per cent by weight of the entire flux, and less than 50 per cent (preferably 25 to 35 per cent). Further the total weight provided by the alkali metal chlorides and the essential fluorides may equal 100 per cent, to the exclusion of other flux components, and preferably is at least 90 per cent when other components not significantly deleterious thereto are included, particularly as hereinafter recommended.

Further, we have discovered that the essential fluorides must be present in certain critical relative amounts in order to produce welding fluxes which will both stabilize the welding arc and formeasily removable slags. For these purposes, it is first necessary that the ratio of the aluminum fluoride to the magnesium fluoride be between about 0.12 to 1. and about 1.2 to 1 by weight. Within these ratios, it is also necessary that the lithium fluoride be present in amount 4 between about 10 and parts per hundred parts by weight of all of the essential fluorides contained in the flux, that said aluminum fluoride further be present in amount between about 10 and 40 parts per hundred as aforesaid, and that said magnesium fluoride further be present in amount between about 10 and 80 parts per hundred as aforesaid. The best fluxes according to our discovery are made with the following fluoride contents: lithium fluoride, about 37 to 55 parts per hundred parts by weight of all of the essential fluorides contained in the flux; aluminum fluoride, about 10 to 30 parts per hundred as aforesaid; and magnesium fluoride, about 22 to 50 parts per hundred as aforesaid, with the ratio of said aluminum fluoride to said sodium fluoride being between about 0.25 to 1 and about 1.2 to l by weight.

In contrast to most prior fluxes for coating aluminum welding rods, which usually contain cryolite, or sodium fluoride and aluminum fluoride in the proportion existing in cryolite, the fluxes described above need contain no sodium fluoride in any form. Further, the fluxes of the invention each contain a substantial amount of lithium fluoride. However, a fluoride combination consisting of lithium fluoride and aluminum fluoride alone (or with magnesium fluoride in amounts smaller than those referred to above) tends to produce a weld slag which is somewhat difficult to remove from the work;' but if in accordance with this invention, an appropriate amount of magnesium fluoride is included, this disadvantage is overcome.

The fluxes, as thus far described, have many desirable characteristics, such as a stabilizing effect on the arc, and a fluxing action which produces easily removable slags. However, further improvements in arc stabilizing and rod adherence properties of these fluxes are obtained, without causing the formation of unduly tenacious slags when the fluxes are used, if sulfur in forms and amounts hereinafter mentioned and any alkaline earth in forms and amounts hereinafter mentioned are included in these fluxes. The sulfur content may be supplied in suitably available form from the group consisting of sulfur, the alkali metal sulfides and sulfates, and the alkaline earth sulfides and sulfates; the total weight of sulfur supplied should be between about ().1 and 2 per cent. The alkaline earth content may be provided by any of the alkaline earth compounds, particularly the al-,

kaline earth chlorides, fluorides, sulfides or sulfates (the sulfides and sulfates mentioned obviously will supply the desired sulfur content as well); the total weight of alkaline earth provided should be between about 0.15 and 5 per cent.

Both the desired sulfur content and the desired alkaline earth content may be most conveniently and effectively provided, within the limits for each as stated above, by incorporating, as a further component in the fluxes described, at least one alkaline earth sulfate in total amount between about 0.5 and 10 per cent by weight (preferably 2 to 6 per cent). Strontium sulfate is most effective, but calcium sulfate is also very effective and somewhat cheaper.

Instead of employing a single flux of the type tion ranges stated for the invention; For example, two fluxbaths mayab'esemployed foricoat; ingi welding? rods; the first producing; an. inner? coating which:.adhereszespecially wellsto=the rod,.

and the second producing an outer coating making. up the necessary overall composition of the flux combination.

Specific examplesofi theifluxes of the invention are given in the following tables and some of' their performance characteristics. are. there-- after mentioned.

Table I.Typical flux compositions (per cent) Table II.C'hlorz'des in typical flares K L M N o P Q Totals: (Table I) 67 52.5 81 63 54 66 68.5

Ratios: KOl/NaCl 1+ 1.5 1 1+ 1 1 1 Table IIL-Fluorides in typical fluxes K L M N o P Q Totals: (Table 1 30 4s 15 30 46.25 30.5 31.5 Parts/100:

MgFz 70 37 4o 40 39 26.25 26.25

Ratios: AlFa/MgFgu 0.21 0.85 0.37 0.37 0.37 0.94 0.94

In addition to the flux compositions given in Table I, hundreds of other flux compositions have been tested and the examples are to be understood as chosen to illustrate various important aspects of the invention without illustrating every composition variation possible. Fluxes K, L, M and fall within the broader composition ranges (as to fluoride contents) stated for the invention. Fluxes N, P and Q fall within the preferred limits for the invention (as to both chloride and fluoride contents), fluxes N and P (most preferred) being two of the most successful fluxes which we have used. All of the fluxes given as examples are capable of maintaining an are that is stable, and that has adequate force. These fluxes may be used as coatings and will adhere very well to the rod, yet the slag produced by these fluxes comes off the work very cleanly with a slight tapping of the work.

The characteristic capacity of the fluxes of the invention for stabilizing a welding arc can readily be determined quantitatively when current (or voltage) records are made by means of a recording meter connected across the welding circuit. Such records have shown the following comparative results. When typical prior art fluxes were used to perform a standard welding operation, the welding current varied about 10 to 15 amperes above and below the mean current value. However, when fluxes of the invention were used, the welding current varied only about 3 to amperes above and below the mean current value. These small variations in welding current, obtained when fluxes of the inven tion were employed, are no greater than the moderate variations found to prevail in the metallic arc welding of steel; they indicate that the fluxes of the invention are significantly improved over: those.v previously employed: in. aluminum welding; since 1- such. stable. are conditions. have? not heretofore. been obtained in. aluminum arc.

welding-I Aswas indicated previously: an aluminum "Weldingirodzmay begivena dry coating-iwhen dipped one;- orsmorev times in one or more dehydrated:

peratures ashigh asuabout 1110-to- 1200 F.', de. pending on the melting point of the flux and that of-the. rod. Likewise,,fiux slurries may be usedtor produce rod coatings, particularly. if an.

absolutely dry: flux is notnecessary. The alue minum'welding rods referred to throughout this.

specification are; of course; made of aluminum or an aluminumbase. alloy selectedfor thewelding and other."characteristics desired, the; Word aluminum being-generally. usedvherein :to designate aluminum of various grades of purity and also aluminum base alloys.

What is claimed is:

1. An aluminum welding flux composed of non-hygroscopic salts, having as the vehicle components constituting the principal part by weight thereof at least two alkali metal chlorides, and having as the essential complementary components constituting at least the major part of the balance of the weight thereof lithium fluoride, aluminum fluoride and magnesium fluoride, said essential fluorides being present in a total amount of at least about 15 per cent by Weight of the entire flux and in relative amounts as follows: the ratio of the aluminum fluoride to the magnesium fluoride being between about 0.12 to 1 and about 1.2 to 1 by weight, the lithium fluoride being present in amount between about 10 and parts per hundred parts by weight of said essential fluorides, said aluminum fluoride further being present in amount between about 10 and 40 parts per hundred parts by weight of said essential fluorides, and said magnesium fluoride further being present in amount between about 10 and 80 parts per hundred parts by weight of said essential fluorides.

2. An aluminum welding flux according to claim 1 in which said vehicle components are sodium chloride and potassium chloride and the amount of potassium chloride is at least equal to the amount of sodium chloride.

3. An aluminum welding flux according to claim 1 having as a further component thereof a total weight of sulfur between about 0.1 and 2 per cent made available from the group consisting of sulfur, the alkali metal sulfides and sulfates, and the alkaline earth sulfides and sulfates, and containing at least one alkaline earth compound providing in the flux a total alkaline earth weight between about 0.15 and 5 per cent.

4. An aluminum welding flux composed of nonhygroscopic salts, having as the vehicle components constituting the principal part by weight thereof sodium chloride and potassium chloride, and having as the essential complementary components constituting at least the major part of the balance of the weight thereof lithium fluoride, aluminum fluoride and magnesium fluoride, said essential fluorides being present in a total amount of at least about 15 per cent by weight of the entire flux and in relative amounts as follows: the ration of the aluminum fluoride to the magnesium fluoride being between about 0.25 to 1 and about 1.2 to l by weight, the lithium fluoride being present in amount between about 37 and 55 parts per hundred parts by weight of said essential fluorides, said aluminum fluoride further being present in amount between about 10 and 30 parts per hundred parts by weight of said essential fluorides, and said magnesium fluoride further being present in amount between about 22 and 50 parts per hundred parts by weight of said essential fluorides.

5. An aluminum welding flux according to 10 claim 4 in which the amount of potassium chloride is at least equal to the amount of sodium chloride.

6. An aluminum welding flux according to claim 4 having as a further component thereof at least one alkaline earth sulfate in total amount between about 0.5 and 10 percent by weight.

7. An aluminum welding flux composed of nonhygroscopic salts comprising about 33 per cent by weight sodium chloride, about 33 per cent by weight potassium chloride, about 15 per cent 8 lithium fluoride, about 7.5 per cent aluminum fluoride, about 8 per cent magnesium fluoride, and about 3.5 per cent alkaline earth sulfate.

MIKE A. MILLER. WARREN E. HAUPIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 922,523 Schoop May 25, 1909 1,550,280 Post Aug. 18, 1925 2,357,125 Miller Aug. 29, 1944 2,456,609 Andrews Dec. 21, 1948 FOREIGN PATENTS Number Country Date 158,890 Switzerland Feb. 16, 1933 849,311 France Aug. 11, 1939 

7. AN ALUMINUM WELDING FLUX COMPOSED OF NONHYDROSCOPIC SALTS COMPRISING ABOUT 33 PER CENT BY WEIGHT SODIUM CHLORIDE, ABOUT 33 PER CENT BY WEIGHT POTASSIUM CHLORIDE, ABOUT 15 PER CENT LITHIUM FLUORIDE, ABOUT 7.5 PER CENT ALUMINUM FLUORIDE, ABOUT 8 PER CENT MAGNESIUM FLUORIDE, AND ABOUT 3.5 PER CENT ALKALINE EARTH SULFATE. 